Question

Name a chemical used to remove permanent hardness of water.

Answer 1

Washing soda $\left({\mathrm{Na}}_2{\mathrm{CO}}_3\right)$

• Washing soda is used to remove permanent hardness of water.
• Washing soda reacts with Calcium sulphate $({\mathrm{CaSO}}_4)$ and Magnesium sulphate $({\mathrm{MgSO}}_4)$ in water to generate $({\mathrm{CaCO}}_3)$ and Magnesium Carbonate $({\mathrm{MgCO}}_3)$ respectively .
• These carbonates are insoluble in water and must be filtered to be separated.

$\underset{\mathrm{Calcium}\mathrm{sulphate}}{{\mathrm{CaSO}}_4\left(\mathrm{aq}\right)}+\underset{\underset{(\mathrm{Washing}\mathrm{soda})}{\mathrm{Sodium}\mathrm{Carbonate}}}{{\mathrm{Na}}_2{\mathrm{CO}}_3\left(\mathrm{s}\right)}\to \underset{\underset{(\mathrm{insoluble}\mathrm{salt})}{\mathrm{Calcium}\mathrm{Carbonate}}}{{\mathrm{CaCO}}_3\left(\mathrm{s}\right)}+\underset{\mathrm{Sodium}\mathrm{Sulphate}}{2{\mathrm{Na}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)}$

$\underset{\mathrm{Magnesium}\mathrm{sulphate}}{{\mathrm{MgSO}}_4\left(\mathrm{aq}\right)}+\underset{\underset{(\mathrm{Washing}\mathrm{soda})}{\mathrm{Sodium}\mathrm{Carbonate}}}{{\mathrm{Na}}_2{\mathrm{CO}}_3\left(\mathrm{s}\right)}\to \underset{\underset{(\mathrm{insoluble}\mathrm{salt})}{\mathrm{Magnesium}\mathrm{Carbonate}}}{{\mathrm{MgCO}}_3\left(\mathrm{s}\right)}+\underset{\mathrm{Sodium}\mathrm{Sulphate}}{2{\mathrm{Na}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)}$